Abortion doctor had been a target before

In this March 23, 2009 file photo Dr. George TIller, enters the courtroom on the first day of his jury trial in Wichita, Kan. Tiller was shot and killed as he entered his church Sunday morning May 31, 2009 in Wichita.

Mike Hutmacher/ The Wichita Eagle/ AP/ File

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The abortion doctor shot and killed while ushering in his church Sunday was among the most controversial providers of abortions in the United States.

In a statement released Sunday, Obama said: "However profound our differences as Americans over difficult issues such as abortion, they cannot be resolved by heinous acts of violence."

Tiller was killed in the foyer of the Reformation Lutheran Church in Wichita just after 10 a.m., police say.

A medical colleague in Wichita told the Los Angeles Times that she thought the crime might have been a reaction to a recent legal victory for Tiller. He was accused of performing late-term abortions without adequate oversight. The jury exonerated him, and local anti-abortion critics might have felt he "got off the hook," said Ann Kristin Niehaus.

Anti-abortion activists worry that the crime is so shocking that it could be politicized and turned against them in the confirmation hearings for Judge Sotomayor. Though the judge's opinions on abortion are not clear from either her rulings or public comments, anti-abortion advocates are concerned that "there would now be an effort to stifle anti-abortion viewpoints during questioning," according to AP.

Tiller's murder is apparently the first abortion-related murder in more than a decade. On October 23, 1998, Barnett Slepian, a doctor who performed abortions in Buffalo, N.Y., was shot and killed in his home.

Tiller began performing abortions in 1973, the year they were legalized by the landmark Supreme Court decision, Roe v. Wade. He had been repeatedly targeted since then, partly because he performed abortions after the fetus was 21 weeks old – the time after which the fetus can live outside the body, according to medical experts.

In addition to the 1985 bombing and the 1993 shooting, Tiller and his clinic were also at the center of a six-week "Summer of Mercy" protest in 1991, which included thousands of demonstrators.